AC evaporator coil frozen: why it happens and the thaw protocol

What to do, in order

1. Switch thermostat to OFF, fan to ON — airflow-only mode melts the coil without cooling it further. Expect 3–8 hours and possibly water around the air handler (towels/pan).
2. Replace the filter while it thaws.
3. After full thaw, restart in COOL with a new filter. If it cools normally: airflow was the culprit — check the blower wheel and duct returns next.
4. If it ices again within hours: refrigerant is low (leak) or the blower is failing. Tech visit — ask for electronic leak detection, not a blind recharge.
5. Water damage check: insulation around the coil and the pan/drain — refreeze cycles crack pans.

Red flags — stop and call a pro

• Ice on the outdoor unit's lines too — system-wide refrigerant issue; running it slugs the compressor, shut it off
• Mold smell after multiple freeze/thaw events — wet insulation in the air handler
• Water dripping through the ceiling below an attic air handler — pan overflow, act fast

Prevention

Filter every 60–90 days, keep returns unblocked, and recharge only with leak repair — repeat freezing means nobody fixed the leak.

This guide is maintained by the ee.ltd editorial team — reviewed for 2026. Browse all home repair guides or compare hvac costs.

Related guides

• AC running but not cooling: 6 checks before you call
• Furnace short cycling (starts and stops every few minutes)
• Thermostat not working: dead screen, wrong temps, no response
• AC won't turn on: what to check before you call

What this repair typically costs

• AC repair cost guide
• AC replacement cost guide
• Furnace replacement cost guide
• Heat pump installation cost guide